Toll operating-circuits.



E. E. HINRIGHSEN @L J. F. TOOMEY.

TOLL OPERATING CIRCUITS.

APPLICATION FILED Nov. 1e, 1911.

Patented May 26, 1914.

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TOLL OPERATING CIRCUITS.

APPLIGATION FILED 11011.18. 1911.

Patented May 26, 1914.

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APPLICATION FILED NOV. I8, 1911. 1,097,86 1 Patented May 26, 1914.

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UNITED STATES PATENT oEEicE.

YORK, N. Y.,

TOLL OPERATINGhCIRCUITS.

specification of Letters Patent. Patented May 26, i914,

Application lred November 18, 1911. Serial N o. 660,968.

and reconnection of the calling operato-rs cord circuit wit-h the tandem trunk will cause a secondapplication of the ringing current to the called line when the tandem trunk is connected with a switching trunk and the called party of the line with which the switching trunk is connected has disconnected his telephone therefrom. This feature consists in so grouping and conn ecting a number of relays with the trunk circuit that certain ones of them which were operated to start the ringing initially are released by the disconnection of the called. partys telephone and the -withdrawal of the calling 4plug from the tandem toll trunk, these relays which are thus released being again operated by conditions caused by the reinsert-ion of the calling plug to again connect ringing current with the called line. The controlling circuit for the operation of the electromagnetic switching means may be a local circuit controlled by a relay associated with the tandem trunk, or may be the one closed in the initial operation of these relays, depending upon whether the switching trunk is connected with a subscribers line or with a private branch eX- change switchboard.

A third feature of this invent-ion relates to the association of apparatus with the tandem toll trunk, whereby the calling operator obtains supervision of the connection as soon as the called party answers the call. Speciically this feature consists in the provision in connection with the tandem trunk of a relay associated with t-he outgoing end thereof and controlling the operation of the supervisory relay in response to circuit kconditions 'controlled by the connection and disconnection of the called partys telephone with the called line. This controlling relay is normally in. series with a high resistance winding of a second relay having also a low resistance winding adapted to be connected in parallel with its high resistance winding by a third relay associated with said tandem trunk and operating when the called subscriber connects his telephone with the line. l

Other features of this invention are the To all whom t may concern p Be it known that we, EDWARD E. HINRICH- SEN and JOHN F. TooismY, citizens of the United States, residing, respectively, at- Alexander, in the county of Morgan and State of Illinois, and at New York, in the county of New York and State of New York, have invented av certa-in new and u seful Improvement in Toll Operating-Circuits, of which the following js a full, clear, concise, and exact description.

This invention relates to a telephone switching system in which the connection between calling and called lines is made through two trunlring lines in series or tandem, and more particularly to a toll trunk line adapted for connection with al type of switching trunk which is itself adapted to be used without change either in connection with a toll cord circuit or with a machine ringing trunk. The toll trunk line will for convenience be referred to hereinafter as the tandem trunk and it is the object of this invention to provide a tandem trunk so equipped as to facilitate the connections between the calling and called line by reducing to a minimum the number ofoperations of the trunking operators in setting up the connections, this being accomplished by having the signaling of the called party and the supervision features for the most part automatic and under control of the calling operator.

One of the features of this invent-ion relates to the organization of the apparatus in the tandem trunk for automatically connecting ringing current with the called line when all manual switching connections are completed. This feature consistsessentially in associating electromagnetic switching apparatus, comprising a plurallty of relays, with the tandem trunk, the relation of said relays to each otherand to the tandem trunk being such that they are controlled jointly by the several switching operations necessary to connect the lines, said electromagnetic switching apparatus in turn controlling the application of ringing current to the called line.

Another feature of this` invention relates to the organization of the apparatus in the tandem trunk, whereby the disconnection be more fully described hereinafter.

details of appara-tus and circuits which Will In the drawings--Figure 1 represents a subscriber' set.y a line circuit therefor terminating in a lo of the apparatus at represents the apparatus at wired in accordance with this invention and adapted for connection with the circuits of Fig. 1; and Fig. 3 represents the circuit wiringof the apparatus at a local station to which a toll trunk is adapted to be connected including the cord and line circuits and a subscriber set circuit.

The three igures when placed together end to end are adapted to torni a continuous connecting circuit from a subscriber' at one end ot the toll line to a subscriber at the opposite end ot' said toll line. In the accompanying description of the operation of this invention, it will be assumed for the sake of convenience and clearness that the apparatus shown .on Fig. 3 located at San Francisco, that shown in Figs. 1 and 2 being located at Oakland.

The subscriber set circuits, line circuit and cord circuit shown are all well known in the art and need not be described in detail. Aside from the removal of the subscribers receiver from the switch hook, there are four switching` operations necessary. These are the connection ot cord circuit S with the calling line through a plug 7 and jack 9, the connection of the cord circuit S with the outgoing end of a tandem trunk 100 through a plug 22 and jack 25, the connection of the tandem trunk 100 with a switching trunk 200 through a plug 201 and a jack 202 and the connection of the switching trunk 200 with called subscribers line through plug 300 and jack 301. The tip and ring springs olf jack at the outgoing end ot the tandem trunk 100 are connected with windings 30, 30 ot' a repeating coil 31, the windings 30, 30 being separated by a condenser 32 and located in inductive relation to windings 33, 33 of the repeating coil 31, which lat-ter windings are separated by a. condenser 34. The repeating coil 31 is located at the San Francisco local exchange and the windings 33 y 33 thereof are adapted to be connected with windings 250, 250 ot' a repeating coil 251 at the Oaklandvtoll otlice. Said windings 250, 250 are separated by a condenser 2^.N and are located in inductive relation to windings 253, 253 of the repeating coil 251, which wind'ngs are separated by a condenser 251. rlhe tip and ring contacts of the jack 202 otl the switching trunk are connected with windings 350, 350 ot' a third repeatingcoil 351 located at the Oakland local exchange, said windings 350, 350 being separated by a condenser' 352 and located in inductive relation to windings 353, 353 of said repeating coil 351, which latter windings are separated by a condenser 35kt. The repeating coils 31 and 351 are inserted in the the local otlice. Fig. 2

"al oilice and the circuit wiring a trunk oliice line for talking purposes while the repeating coil 251 is used for signalingpurposes.

The invention may be best described by -following the operation of the circuits and apparatus during the setting up ot a connection between a subscriber in one town, say San Francisco, and a subscriber in another town, say Oakland. Assuming then that a subscriber A at San Francisco desires to converse with a subscriber B at Oakland, subscriber A will remove the receiver 1 from the switch hook 2, thus coinpleting a circuit over the two line wires 3 and 4 through a line relay 5. The operation of the line relay 5 will light line lamp 6 and thus indicate to the local operator at the particular exchange in San Francisco with which the calling subscriber is connected, that such subscriber is calling. The local exchange operator responds to the sig nal of the line lamp by inserting an answering plug 7 of the cord circuit 8 into a line jack 9 and depressing a key 10 which connects her telephone set 12 with the tip and ring wires 13 and 14 of the cord circuit. The insertion of the plug 7 into the ack 9 completes a circuit from battery 2O through a supervisory lamp 15, the sleeve contacts of the plug and jack 7 and 9 and a cut-oti' relay 1G to ground. Sufficient current will flow in this circuit to light the supervismy lamp 15 and operate the cut-oft relay l0. the operation of the cut-off relay opening the circuit of the line relay 5 and extinguishing the line lamp G. rlhe insert-ion of the plug 7 into the jack 9 will also complete circuit through a supervisory relay 17, the operation of which shunts the supervisory lamp 15 with a low resistance 1S. This will oxtinguish the lamp 15, but will retain the eutoit relay 1G energized. rlhe local operator at San Francisco upon determining. that party A desires to talk with party B at Oakland, so advises the toll operator at Oakland over an order wire circuit which is not shown as it is not a part of this invention and is well enough known in the art to require no description here. The toll operator at Oakland assigns a trunk line to the local operatorat' San Francisco, which is the one terminating in jack 25 in front et said local operator. At the same time the toll ope ator at Oakland will get inte communication over an order wire circuit with the switching operator at the Oakland exchange with which the line of the desired party connects. T he switchii'ig exchange operator then assigns a trunk to the Oakland toll operator and inserts the plug 300 of that trunk into j ack 301 in which the line of party B terminates. Upon receiving the trunk assignment from the Oakland switching operator, the Oakland toll operator inserts the plug E201 of the trunk she assigned the San Francisco local operator into the jack 202 of the aspart automatic connections have all signed trunk between Oakland toll and Oak. land local. The assignment of trunks and setting up of the connections is the only operation necessary on the part of the Oakland operators until the conversation has been completed and disconnection is made, the remainder of the operations being for the most and controlled by the San Francisco local operator and the subscribers.

Assuming now that the manual switching been established, the succeeding operations for completing the signaling circuit andi signaling Will be as follows: Upon the insertion of the plug 22 into the jack 25 at the outgoing end of the tandem trunk, a circuit will be completed from battery 2O through supervisory lamp 26, resistance 27, sleeve contacts of the plug 22 and jack 25, conductor 312 and winding of relay 28 to ground. Current in this path Will energize the relay 28, closing front contacts 29, 29 and connecting conductors 35, 35 With line conductors 36, 36 which are connected With the windings 250, 250 of the repeating coil 251 at the toll trunk olice in Oakland. This completes a circuit from battery 20 through one Winding of a relay 37, conductor 38, one Winding 33 of repeating coil 31, conductor 35, one contact 29 of relay 28, the corresponding line conductor 36, one Winding 250 of repeating coil 251, conductors 39 and 40, a high resistance winding 41 on a relay 42, conductor 43, the other Winding 250 of the repeating coil 251, correspond-V ing line conductor 36, the other contact 29 of the relay 28, conductor 35, the lother Wind ing 33 of the repeating coil 31, conductor 44 and the other Winding of the relay 37 to ground. Current over `this path energizes the relay 42 through its Winding 41, but owing to the high resistance of said winding 41 insufficient current will flow to energize relay 37. The operation of relay 42 closes its front contact 45 and completes a circuit for a relay 50 Which may be traced from battery 51 through Winding of relay 50, conductor 52, conductor 53 and front contact 45 of relay 42 to ground. Current in this path operates the relay 50 to close contacts 54 and 55 and open contact 56 and will complete a circuit for lighting a lamp 58. This circuit may be traced from battery 51 at the plug end of the tandem trunk, conductor 59, normally closed contact of a relay 61, conductor 62, contact 54 of relay 50, conductor 63 and lamp 58 to ground. The lighting of the lamp 58 will indicate to the toll operator that the San Francisco local Y operator has plugged into the proper trunk.

When the tandem trunk operator inserts the plug 201 into the jack 202 of the switching trunk the relay 61 will be energized by current in a circuit traced from the battery 51, winding of relay 61, conductor 65, sleeve contacts of the plug and jack 201 and 202 through resistance coil 66 to ground. The the relay 61 will open the con operation of tact 60, thus interrupting the circuit for the lamp 58 previously traced and will close contacts 67 and 68. Aside from the relays 42, 50 and 61 already mentioned, there are associated with t-he tandem trunk vat the incoming end thereof relays 70, 7l, 72, 73, 74, 75, 76, 77 and 78, which, in conjunction with relays 80, 81, 82, 83, 84, 85, 86, 87, 88 and 89 associated with the connecting trunk, operate in the sequence of their numbers in the separate circuits to ring the called subscriber and give the proper disconnect signals when the conversation is completed. The relay 86 serves as an electromagnetic ringing key to connect ringing current with the called line.

Referring irstto the means for signaling the called subscriber, the operation Will be as follows: After the operation of the relays 50 and 61 hereinbefore referred to, there Will be completed a circuit for the relay which may be traced as follows: from battery 90 at the Oakland local exchange through one Winding 91 of the relay 80, conducto'r 92, normally closed contact 93 of relay 81, conductor 94, conductor 95, one Winding 350 of repeating coil 351, conductor 96, ring contacts of jack and plug 202 and 201, conductor 97, normally closed contact 98 of the relay 7 6, conductor 99, one Winding 253 of the repeating coil 251, conductor 102, conductor 103, Contact 55 of relay 50, conduct-or 104, back con-tact 105 of the relay 71, conductor 106, Winding of relay 70, conductor 107, conductor 108, the other Winding 253 of repeating coil 251, conductor 109, normally closed contact 110 of the relay 76, conductor 111, cont-act 68 of relay 61, conductor 112, tip contacts of the plug and jack 201 and 202, conductor 113, the other Winding 350 of repeating coil 351, conductor 114, normally closed contact 115 of relay 81, conductorll and through Winding 117 of relay 80. The current in this path Will energize both relays 70 and 80. The operation of relay 70 closes its front contact 120 and completes circuitsfor relays 71 and 72. The circuit for rela)7 71 Will be from battery 51 through Winding of relay 71, conductor 121, conductor 122, front contact 120 of the relay 70, conductor 123, conductor 53 and front contact 45 of relay 42 to ground. The circuit for the relay 72 will be from battery 51, through one Winding 125 of the relay 72, conductor 126 to point 127, conductor 128, normally closed contact 129 of relay 74, conductor313, conductor 122, front contact 120 of relay 70, conductor 123, conductor 53, front contact 45 ofv relay 42 to ground.

When relay 71 operates'it opens back contact 105 and closes contacts 130 and 131. With the closing of contact 131 a locking circuit is completed for relay 7l .which may be traced from battery 51 through the winding of relay 71, conductor 121, contact 131, conductor 132, conductor 53, contact 45 of relay 42 to ground. The operation of relay 72 will close its liront Contact 133 which is connected through conductor 134 with one terminal of the winding of the relay 76, the other terminal of which is connected to ground. There will be no current through this relay, however, inasmuch as the point 127 is at this time ground potential. The closing of the contact 130 of the relay 71 will connect the relay 73 with the line wires 99 and 109 in shunt of the condenser 254,

the circuit being as follows: from line 109 at one side of the condenser 254, conductor 108, conductor 135, winding of relay 73, conductor 136, Contact 130 of relay 71, conductor 104, contact 55 of relay 50, conductor 103 and conductor 102 to the line 99 at the other side of the condenser 254. This prepares a path through the winding of the relay 73 over which current may tlow from the switching trunk as will be hereinafter explained.

Referring now to the sequence of operations of the relays in the switching trunk, it will be noted that when the relay 80 operates, it opens a back contact 140 and closes a front contact 141. The closing of the front contact 141 completes a circuit from the 48 bolt battery 145, contact 141, conductor 146 through one winding 147 ot relay 81, conductor 148, normally closed contact 149 of the relay 83, lamp 150 to the battery 90. The battery 90 being a 24 volt one, there will be a pressure of 24 volts over this circuit, which will energize the relay 81 and light the lamp 150. The operation of relay 81 will open contacts 93 and 115 and close contacts 152 and 153. The opening of contacts 93 and 115 opens the circuit over which relay was originally energized, while the closure of contacts 152 and 153 completes a local circuit for the relay 80 through a resistance 154. lVhen the plug 300 is in the jack 301, there will be a circuit for relays 82 and 83 which may be traced from battery at 90, winding of relay 82, conductor 160, winding of relayv 83, conductor 161, sleeve contacts of plug 300 and jack 301, conductor 162 and cut-*0E relay 163 to ground. The current in this path will energize relays 82 and 83. The operation of relay 82 will open its back contact 165 and close its front contact 166, which is connected with a conductor 167 leading to a ringing generator 168. This will have no etteet, however, as the path for ringing current is open at another point which is not closed until later. The operation of relay 83 opens contact 149 and closes contacts 170 and 171. The opening of contact 149 opens the energizing circuit for relay 81, thus opening the contacts 152 and 153 and closing contacts 93 and 115. The closing of contact 170, however, completes a circuit for relay 84 which may be traced from the 48-Voltbattery 145 through winding of relay 84, conductor 172, conductor 173, coutact 170 of relay 83, the lamp 150 and the 24 Volt battery 90 to ground. This will operate the relay 84, but on account of said relayvbeing ot' high resistance will not light the lamp 150. The contacts 93 and 115 ot relay 81 being again closed, there will be a tlow of current through the windings of the relayl 80 and back to the tandem trunk over practically the same path that it took When relay 70 was energized, except that this time, instead of'going through the back contact of relay 71 and conductor 106 to the winding of relay 70, it will pass through front contact 130 of relay 71, conductor 136, winding of relay 73, conductor 135 and from there back to ground, the remainder ot the path being the same as previously traced for relay 70. The current in this path will energize the relays 73 and 80, the local circuit of relay 80 through the resistance 154 having been opened by the opening of the contacts 152 and 153 when relay 83 pulled up and opened the circuit ot' relay 81. The operation of relay 73 closes front contact 176 and completes an energizing circuit for relays 74 and 75, which circuit may be traced from battery 51 through winding 177 or' relay 7 5, conductor 178, winding of relay 74, conductor 179, conductor 180, front contact 176 of relay 73, conductor 181, back contact 182 of relay 70, conductor 123, conductor 53 and front contact 45 of relay 42 to ground. The current in this path causes the operation of relays 74 and 75. The operation of relay 74 opens contacts 129 and 183 and closes contact 184, completing a locking circuit Jfor the relays 74 and 75, which may be traced from battery 51, winding 177 of relay 75, conductor 178, winding of relay 74, conductor 179, contact 184, conductor 185, conductor 53, contact 45 of relay 42 to ground.A The operation of relay 75 closes contacts 186 and 187 and completes` a locking circuit for itself through winding 190 thereof, this circuit being traced from battery 51, conductor 59, contact 67 of relay 61, conductor 191, contact 187 of relay 75, conductor 192, winding 190 of relay 75 and conductor 193 to ground.

The opening of contact 129 of the realy 74 will remove the ground from conductor 128 and cause the currentto flow through both windings of the relay 72, contact 133, con duetor 134 and winding of relay 76 to ground. This will be but an impulse, however, as the two windings of the relay 72 are connected ditl'erentially and this relay will be released by this flow of current, not, however, before the operation of the relay 76.

lVhen the relay 76 operates, it opens contacts 98 and 110, closing contacts 205 and 206 and completing an `energizing circuit from' generator 207 for the relay 85 at Oakland switching exchange. This circuitmay be traced from generator207, conductor 208, lamp 209, conductor 4210, contact 205 of relay 76, conductor 97 ring contacts o'f lug 201 and'jack 202, conductor 96, one winding 350 of repeating coil 351, conductor 95, con denser 211, winding of relay 85, conductor 212, the other winding 350 of repeatin coil 351, conductor 113 tip contacts of jac 202 and plug 201, conductor` 112, contact 68 of relay61, conductor 111 and contact 206 of relay 76 to ground. The operation of relay 85 closes its front-contact 215 and completes an energizing circuit for relays 88, 87, 86 andl 81 in series, which circuit may be traced as follows: from battery 90, conductor 216, winding of relay 88,'conductor 217, winding of relay 87, conductor 218, winding 219 of relay 86, conductor 220, contact 215 of relay 85, conductor 222, through winding 223 of relay 81 to ground. Current in this circuit operates relays 88, 86, 87 and 81. The operation 'of relay 88 closes a locking circuit for the relays 86, 87 and 88, which may be traced 'from battery 90, conductor 216 winding of relay 88, conductor 217, winclin of relay 87, conductor 218, winding 225 o relay 86, conductor 226, contact 227 of relay 88, conductor 228, conductor 229, back contact 230 of relay 89, conductor 231 and con tact 232 of relay 84 to ground. This circuit remains closed until opened at the back contact 230 of relay 89 as will later appear. When the relay 86 operates, a circuit is conipleted fromthe ringing generator 168 through a bell 236 at the subscribers station B. This circuit may be traced from generator 168, conductor 167, front contact 166 of relay 82, conductor 239, winding of relay 89, conductor 240, front contact 241 of relay 86, 'conductor 242, ring contacts of plug 300 .the switch hook at and jack 301, line wire 243, bell 236, condenser 244,line wire 245, tip contacts of jack 301 and plug 300, conductor246, front con-v tact 171 ofrelay 83, conductorv 264, and front contactv247 of relay 86 to ground. The lcurrent in this circuit will ring the bell 236, but owing to the high impedence of the bell magnets will not operate the relay 89 as long as subscriber station B -remains on the hook. When the subscriber atv station B answers the ring, however, the operation of the receiver switch hook shuntsy the bell 236 and the current through this shunt path will be suicient to energize the relay 89 to open the contact 230 thereof. The opening of the contact 230 interrupts the holding circuit of relays 86, 87 and 88. lhen relay 86 is denergized, it opens front contacts 241 and 247 and closes back contacts255 and 256, thus interrupting the ringing circuit and completing the talking circuitv over the switching trunk.

ond energization of relay 81,\which occurs upon the closure of contact 215 of relay 85,

is onlym'omentary and instant the local circuit This relay 80 is made slow-releasing by means of a copper shell over the core, and although 81 falls backalmost immediately, there will be a short period of vtime intervene. before relay -80 drops back. During this intervening time, however, the relay 76 will have been denergized, thus closin con` tacts 98 and 110 and completing the original energizing circuit of the relay 80 in series withl the relay 73 in the tandem trunk until the relay 81 is again energized. The third energization of relay 81 occurs when the party at station B removes his receiver from the hook for the purpose of answering vthe call. l/Vhen this cuit is completed from the 48 volt battery 145, through contact 141 of relay 80, conductor 146, winding 147 of relay 81, conductor 257, one winding 353 of repeating coil `351, conductor 2,58, contact 256 of relay 86, conductor 242, ring contacts of plug 300 and jack 301, line wire 243, primary 259 of induction coil 260, Contact 261 of switch hook 262, transmitter 263, line wire 245, tip contacts of jack 301 and plug 300, conductor 246, contact 171 of relay 83, conductor 264, contact 255 of relay 86, conductor 265, the other winding 353 of repeating coil 351, co-nductor 222 and Winding 223 of relay 81 to ground. The operation of relay 81 by current over this path openscontacts 93 and 115, thus interrupting the circuit through the relay 73 of the tandem trunk. I When relay 73 is denergized, it will close its back contact 270 and complete a circuit for the relay 77 which may be traced as follows: from battery 51 at the plug end of the tandem trunk, conductor 59. contact 67, yconductor 191, conductor 271, contact 186 of relay 75, conductori272, conductor 273, winding of relay 77, conductor 274, back contact 270 of relay 73, conductor 181, back contact 182 of relay 70, conductor 1,23,- conductor 53 and contact 45 of relay 42 to ground. The operation of relay 77 closes its front contact 276 connecting conductors 277 and 278 together and thus placing the low resistance winding 279 of the relay 42 in parallel with the high resistance winding 41 thereof. With these two windings in parallel, there will be sufficient current flow through the rela)7 37 at the outgoing end of the tandem trunk to energize said relay 37. The operation of the relay 37 closes its front contact 285 and completes a circuit for the supervisory relay -19' in the cord circuit. This circuit may he traced from the bridged battery 20 closes only for an of the relay 80.

-in the cord circuit through conductor 14,

occurs an energizing cirf relay 19, conductor 286,

287, 287, ring contacts of plug 22 and jack 25, conductor 288, one winding 30 of repeating coll 31, conductor 290 including resistance 291, contact 285, conductor 292, the other winding 30 of repeating coil 31, conductor 293, t1p contacts of jack 25 and plug 22, key contacts 294, 294, and conductor 13 to the ground side of the bridge battery 20. This operates the supervisory relay 19, closing contact 295 and shunting lamp 26 with ow reslstance 296, thereby causing said lamp to be extinguished and indicating to the local operator at San Francisco that the called party at Oakland has answered. Assuming now that the subscriber at Oakland hangs up his receiver either at the completion of the conversation or for any other reason, this will be indicated at the San Francisco local exchange by the illumination of the supervisory lamp 26 through the following operation of the circuit apparatus The hanging up of the receiver at subscriber station B will open the contact 261, thus interrupting the energizing circuit last traced for the relay 81. The denergizing of this relay will close the contacts 93 and 115, thus closing the energizing circuit for the relay 73 hereinbefore traced. The operation ofthe relay 73 opens contact 270,

the winding of the closed key contacts interrupting the circuit of the relay 77 andg opening contact 276 of said relay 77. The opening of contact 276 takes the low resistance winding 279 of relay 42 out of the energizing circuit of the relay 37 at the outgoing end of the tandem trunk, thusincreasing the resistance of this circuit to such an extent that said relay 37 fallsjback and opens its contact 285. The opening of contact 285'interrupts" the` circuit ofthe supervisory relay 19 which in turn interrupts the circuit of" the shunt resistance 296 and perinitsthe lamp 26. to`- light. lIf now the San- Francisco operator desires to re-ring'the Oakland subscriber, she 'does so by withdrawing plug 22 from thev jack 25 and re-inserting it. The withdrawal of the plug V22 from the jack-'25 releases relays 28, 42, 50, 7173-and 74 in the tandem trunk anderelay 8O of the switching trunk. The re-insertion of plug 22 into the jack 25 operates the relays the sequence-"described in the .operation'ffofg.the-system to again ring the subscriber-at-*station B.

The Switching-tpugnk@Q00 ,is adaptedfof connection witha private branch exchange trunk as: well as with a.A subscribers line. When'the switching. trunk 200 is connected with a private branch exchange trunk, there will bea holding coil across the line at the private branch exchange which will prevent the release of the relay 81 when the called subscriber hangs up his receiver. The relay 81 remaining energized, will prevent the closing of the contacts 93 and 115 and the consequent energization of rela by current in the path originally trace fo;` the energization of this relay. It will be seen, therefore, that in order to trip the ringing by withdrawing and re-inserting the plug 22 into the jack 25, there must be some other source ofcurrent for energizing the relay 70 than that provided by the battery 90 of the switching trunk at the Oakland local orifice. This is provided for by the relay 78 at the incoming end of the tandem trunk 100 at Oakland toll otiice.

The operation of the apparatus upon a re-ring will under these conditions be as follows: When the operator at San Francisco re-inserts'plug 22 into the jack 25, the relay 28 will operate, completing the circuit for the relay 42. The operation of relay 42 will complete the energizing circuit for relay 50 and also for the relay 78, the latter circuit being traced from battery 51 at the plug end of the tandem trunk through conductor 59, contact 67 of relay 61 which was not released by the withdrawal of plug 22 from jack 25, conductor 191, conductor 271, contact 186 of relay 75, conductor 272, conductor 306, winding of relay 78, conductor 307, contact 183 of relay 74, conductor 185, conductor 53 and contact 45 of relay 42 to round. Current in this path will energize the'relay 78 and close contacts 308 and 309 thereof. The closure of contacts 308 and 309 completes a circuit for the relay 70 which may be traced from battery 51, through contact 308 of relay .78, conductor 310, conductor 107, winding of relay 70, conductor 106, back contact '105 of relay 71, conductor 104, contact 55 of relay 50, conductor v103, conductor 311 and contact 309 of relay 78 to ground. The current in this path will energize relay 70 and thc relays Aof the tandem trunk and switching trunk willv 'operate in the sequence and over the circuits originally-traced to start the ringing and signal the private branch exchange operator.

The relay 70 is provided with a copper head 325 which makes this relay slow-acting the purpose of this being to prevent t-he energization of the relay 73 in case the toll operator plugs into the jack 202 before the switching operator has made connections with the called subscribers line. As will be noted from the drawings the insertion of the plug 201 into the jack 202 will cause an impulse of current to flow from the battery 90 at the switching trunk back over the 'line and through the relay 70. This impulse is only for an instant, however, and will sufiice to operate the relay 70, but'the relay 81 will have operated before the relays 71 and 72 have closed their front contacts, thereby removing the battery 90 from circuit therewith. y

The switching trunk shown in Fig.I4 1 is arranged for connection with lines in which the party is called'by either one or two rings and 'is adapted to automatically take care of these two classes of ringing. For this pur- 300 is inserted into a jack 301 in pose there is provided `in addition to the relay 82 a second relay 330 which is dependent for itsoperation u on the non-operation of the relay 82. IA there is no' resistance other than that of the cut-off relay 163 in the sleeve wire 162 of the jack 301 then the relay 82 will beoperated upon the connection of the plug and yjack 300 and 301 and the ringing current will have the path previously traced. If, however, the plug which there is additional resistance in .thesleeve wire 162, the relay 82 will notvbe operated Iand a circuit will be closed for therelay 830 upon the operation of the4 relays 85, 86, 87 and 88. The o-peration of relay 330 will close a path for interrupted ringing current which will be through the back cont-act of the relay 82 and over the path previously traced. This forms no part of the invention, however, and the specific operation and circuits need not be herein traced.

When vthe plugs are removed from. the

jacks in making disconnection, the relays will all ret-urn to their normal or unoperated position preparatory to another call. While this invention has been described in connection with a particular class of toll line business, it is to be understood that the invention is not limited to this particular class, but may be applied to any class of toll business, although not recommended for use in connection with lines of too great length on account of the cost of installation.v

We claim:

1. The combination with telephone trunk lines and connecting switches at each terminal of each of said trunk lines uniting said trunk lines with each other and with other lines, of an electromagnetic ringing key associated with one of said trunk lines, an energizing circuit for said ringing key and means in each of said trunks controlled jointly by the vconnect-ion switches at the terminals of said trunk lines for closing the circuit for said ringing key.

2. The combination with telephone trunk lines and connecting 'switches at each terminal of each ot said trunk lines uniting said trunk lines with each other and with other lines, of an electromagnetic ringing key associated with one ,of said trunk lines, electromagnetic switching means associated with the other of said trunk lines controlling the operation of said ringing key, said 'electromagnetic switchlng means belng under the joint control o f the connection switches at both ends of sa1d trunk lines.

the line before the` relay 73 is brought into under the 'joint control of the connecting switches at the ends of said trunk lines to close a circuit for said relay including said alternating current source.

4. The com bination with a calling and a called line, of aY telephone switching trunk liue,; a tandem trunk line, connection switches at each terminal of said trunk lines for uniting them with each other and with che calling and called lines,an electromagnetic ringing lrey-v` associated with said switching trunk line, electromagnetic means comprising a plurality of relays associated with each of said trunk lines and control- /ling theoperation of said ringing key, a circuit controlling certain ones only of said relays completed by the connection switches uniting said tandem trunk with the calling line and 'with aid switching trunk and a circuit controlling the operation of the remaining ones olf said relays controlled by the connection ing trunk with the called line.

5. The combination with a calling and a called 1ine,'of a switching trunk line, a tandem trunk line, connection switches at each terminal of said t-runklines uniting them with each other and with the called and calling lines, respectively, an electromagnetic ringing key associatedwith said switching trunk, electromagnetic` switch ing means comprising a plurality of relays cont-rolling the operation of said ringing key,I a slow-acting relay included in said switches uniting the switcbelectromagnetic switching means and controlling the operation of certain ones only of said relays, a 'circuit for said slowacting relay under the joint control of the connect-ion switches uniting said tandem trunk with the calling line and with the switching 1 trunk, a second relay included in said electromagnetic switching means and controlling the operation of the lremaining onesof said relays, and a circuiti'or said second relay under the joint control of the said slow-actingrelay andthe connection switches uniting the switching trunk with the called line.

6. The combination with trunking lines, a cord circuit and a called line, oi.k connection switches for unitingsaid trunk lines with each other and with said cord circuit and called line, a supervisory signal associated with said ycord circuit and means in each of said trunk lines for controllmg tbe circuit of said supervisory signal, said means being rendered operative-,by electrical conditions established by the Jconnection of the called telephone with thev line.

7. The combination with. telephone trunking lines, a connecting cord circuit and. a called line, of connection switches for uniting said trunk lines with each other.l with said cord circuit and with said called line, a supervisory relay associated with said cord circuit, electromagnetic switching means' in each ofsaid trunk lines controlling the operation of said supervisory signal, and a circuit controlling the operation of said electromagnetic switching means established over the called line.

8. The combination with a called line, a connecting cord circuit and switching and tandem trunks for uniting said called line and said cord circuit, vof a supervisory signal associated with said cord circuit, a. relay associated with the outgoing end of said tandem trunk controlling the circuit of said supervisory signal, electromagnetic switching means in each of said trunk lines controlling tlie operation of said relay and a circuit cont-rolling the operation of said electromagnetic switching means completed over the called line.

9. The combination with a called line, a connecting cord circuit, and switching and tandem trunk linesffor uniting said called line and said cord circuit, of a supervisory relay associated with said cord circuit, a relay associated with said tandem trunk con trolling the operation of said supervisory relay, a second relay having a high and low resistance winding, a circuit for said controlling relay including the high resistance winding of said second relay, electromagnetic switching means for connecting the high and low resistance windings of said second relay in parallel, and a controlling circuit for said switching means completed over the wires of said called line.

Y 10. The combination with a called line, a connecting cord circuit and switching and tandem trunk lines for uniting said cord circuit and said called line, of a supervisory relay associated with said cord circuit, a relay associated with the outgoing end of said tandem trunk for controlling the operation of said supervisory relay, a second relay associated with said tandem trunk and having a high resistance windingvand a low resistance winding, a circuit for said controlling relay'including the high resistance winding of said second relay, a third relay associated with said tandem trunk adapted to connect the high and low resistance windings of said second relay ins parallel, a relay associated with saidl switching trunk controlling the operation of said third named relay, and a circuit for said switching trunk relay completed over said called line.`

11. The combination with telephone trunk lines and connecting switches at each terminal of each of said'lines uniting said trunk lines with each other and with other lines, of an electromagnetic ringing key associated with one of said trunk lines, an energizing circuit for said ringing key, means in each of said trunks controlled by the joint action of the connection switches at the terminals of said trunk lines for closing said energizing circuit, means for opening the circuit of said key, a` circuit controlling said key circuit opening means completed over one of ,said lines, and means controlled by a second operation of the connection switches at one terminal of one of said trunk lines for again operating the circuit closing means ot said ringing key.

12. The combination with telephone trunk lines andconnection switches at each terminal of each of said trunk lines for uniting them with each other and with other lines, of an electromagnetic ringing keyiassociated with one of said trunk lines, an energizing circuit for said ringing key, electromagnetic switching means associated with each of said trunk lines controlling the circuit of said ringing key, said electromagnetic switching means operating under the joint control of all of said connection switches, means for opening the circuit of said ringing key, a

circuit for said circuit opening means completed over one of the lines with which said trunks are connected, and means cont-rolled by a second operation of the connection switches at one terminal of one of said trunk lines for again operating said electromagnetic switching key.

13. The combination with a switching trunk line, a tandem trunk line, a connecting cord circuit and a called line, of connection switches uniting said trunk lines with each other and with said cord circuit and a called line, a ringing key associated with said 1 switching trunk, means associated with said tandem trunk operated@ by said connection switches controlling an energizing circuit for said key, means for releasing said key a circuit for said releasing means controlle over the called line, and means controlled by the connectionJ switch uniting the tandem trunk and the cord circuit for again closing the energizing circuit of said ringing key.

14. The combination with a switching trunk line, a tandem trunk line, a cord circuit and a called line, of connection switches uniting said trunk lines with each other and with said cord circuit and called line, an electromagnetic ringing key associated with said switching trunk line, electromagnetic switching means associated with each of said trunk lines and operating under the joint control of all of said connection switches to operate said ringing key, means for releasing said ringing key, a circuit for said reizo switches controlling said switching means.

In witness whereof, we hereunto subscribe our names this 15th day of November, A. D., 1911.

EDWARD E. HINRICHSEN. JOHN F. TOOMEY.

Witnesses to signature of Edward E. Hinrichsen:

F. P. MoINTosH, S. B. WILLIAMS, Jr.

Witnesses to signature of John F. Toomey:

F. P. McINTosH, ROBERTS. SUTIJFFE.

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